Exoplanets: the census

At a glance

Key points

Small worlds turn out to be common.

• 6,400+ confirmed worlds
• Three in four found by transit
• Sub-Neptune-sized worlds are the largest group found

How planets are found

A transit dims a star by the planet's share of its disc: about 0.008% for an Earth crossing the Sun, 1% for a Jupiter. The radial-velocity method measures the star's wobble instead, but gives only a minimum mass. Microlensing, direct imaging and timing methods account for the rest.

A biased sample

The census reflects how planets are found as much as what exists. Transits favour large planets on short orbits, because they block more light and cross their stars more often; radial velocity favours massive planets close in. Hot Jupiters are therefore over-represented, while Earth-sized planets on year-long orbits around Sun-like stars are barely sampled. Survey statistics must correct for these biases before saying how common any kind of planet really is.

The habitable zone, with caveats

The habitable zone is the range of distances where a planet with a suitable atmosphere could keep liquid water on its surface. Being in it is not the same as being habitable: JWST is finding that rocky planets close to small red dwarfs often have no thick atmosphere at all.

What we still don't know

Whether any rocky planet around a red dwarf keeps an atmosphere, and how common true Earth analogues around Sun-like stars are.

Missions

1. 2009–2018

   Kepler / K2

   NASACompleted

   Transit survey that showed small planets are common.

2. 2018–

   TESS

   NASAActive

   All-sky transit survey; over 1,000 confirmed planets.

3. 2021–

   James Webb Space Telescope

   NASA / ESA / CSAActive

   Infrared observatory at Sun–Earth L2, about 1.5 million km from Earth.

   Mission page (opens in a new tab)

Related entries

• TRAPPIST-1Seven Earth-sized worlds · about 40.5 light-years
• Proxima Centauri bThe nearest exoplanet · 4.24 light-years
• K2-18 bA sub-Neptune at the centre of a biosignature debate

Sources

1. NASA Exoplanet Archive (IPAC/Caltech) (opens in a new tab)
2. IPAC: the Exoplanet Archive hits 6,000 planets (opens in a new tab)
3. NASA Exoplanet Archive: PSR B1257+12 overview (opens in a new tab)
4. NASA Exoplanet Archive: 51 Peg overview (opens in a new tab)

Last reviewed 10 Oct 2026 against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.